Heating unit



May 7, 1963 w. D. KELLY 3,089,016

HEATING UNIT Filed Aug. 17, 1959 2 sheetssheet 1 2f/mwa /fm a 269 Moy/vz@ 7;

May 7, 1963 w. D. KELLY 3,089,016

HEATING UNIT Filed Aug. 17, 1959 2 sheets-sheet 2 nlm .'ibl@ Patented May 7, i963 3,089,0l6 HEATING UNET William D. Kelly, Western Springs, lll., assigner to Ferro Corporation, a corporation of Ohio Filed Aug. 17, 1959, Ser. No. 833,997 8 Claims. (Cl. 2319-19) This invention relates to a heating unit and more particularly to a fin con-struction and mounting for a tubular heating lunit with an electrical heating element disposed inside an elongated tube and surrounded by compacted insulating material.

The usual method of applying radiating fins to tubular heat transfer elements is to `slide iins having a loose t with the tube into place thereon and then expand the tube, as by air or hydraulic pressure, lso that it engages the tins holding them firmly in place.

Certain types of electrical heating units have an electrical element, as a. length of resistance wire, extending through the length of the tube. The space around the electrical element is lfilled with an electrical insulating material, generally in granular form. As a step in the manufacture of such an element, the tube ends are closed and the material within the tube compacted, as iby swaging the tube to a smaller diameter. Obviously, the ns must be mounted after the tube has been swaged; and pressure expansion cannot be used.

A principal object of this invention is the provision of a novel lin construction, by virtue of which tins are mounted on the tube and have `good heat transfer contact with it, after the tube has been swaged.

One feature of the invention is the provision of a lin for a tubular heating unit, comprising a plate of heatconductive material having a tube-receiving opening therein surrounded by a collar portion, the collar portion having a substantial area in intimate contact with the tube.

Another feature is that the fin has a fold formed therein extending outwardly from the collar providing resilience or springiness in the fin, the collar tightly gripping the surface of the tube.

A further `feature is that a plurality of fins are frictionmounted on the tubular element and keyed together to insure proper alignment. This is preferably accomplished by nesting the yfolds in adjacent fins. Yet another feature is that the ns are provided with portions extending outwardly therefrom and engaging the surface of the next adjacent lin maintaining the spacing therebetween, preventing the fold of each fin from entering the fold of the adjacent iin and loosening its engagement with the tube.

Still another feature of the invention is the provision of an end member for a tubular heating element, the end member having a cup-shaped configuration with a dimple or depression formed in the closed end of the cup. The end member is secured in the tube with its closed end extending inwardly and the dimple extending outwardly. Upon swaging or compression of the tube, the dimple deepens, relieving forces which tend to dislodge the end member from the tube.

Further features and advantages of the invention will readily be apparent from the following specification and from they drawings, in which:

FIGURE l is a plan view of a unit with lins mounted thereon and embodying the invention;

FIGURE 2 is an enlarged section taken axially through the tube of FIGURE 1;

FIGURE 3 is an enlarged fragmentary detail illustrating the nested relationship of the fins;

FIGURE 4 is an elevational view looking down on FIGURE l;

FIGURE 5 is a plan View of a modified `iin construction.

FIGURE 6 is an enlarged fragmentary end view of a lin blank following the first forming step;

FIGURE 7 is a side view from the left of the -fin blank of FIGURE 5;

FIGURE 8 is an end view of the iin blank of FIG- URE 5;

FIGURE 9 is an enlarged fragmentary section of the end portion of the tubular heating unit, before swagin-g;

FIGURE l() is a view similar to FIGURE 9 afterl Swaging;

FIGURE l1 is an enlarged fragmentary section of a modified iin; and

FIGURE l2 is a sectional view taken generally along the line l2-l2 of FIGURE l1.

The heat-radiating iin construction is illustrated herein as applied to tubular heating units with electrical heating elements therein and it is particularly adapted for such units. However, it can be .used for other types of tubes as those through which a huid heat-transfer medium is circulated, as will be apparent.

Turning now to FIGURES 1-4 of the drawings, a tubular unit Ztl having an electrical heating element Z1 therein, is illustrated. A plurality of heat-radiating ns 22 are mounted on the tube. In practice fins 22 cover the entire length of the tube 2li; `for clarity and simplicity only a portion of the tins are shown. Each of the ns has a substantial surface area (FIGURE 6) with a tube receiving opening 23 located centrally therein. Surrounding the opening in which the tube 2li is received collar 24 extends outwardly from the surface of fin 22, and has a substantial surface area in intimate frictional contact with tube Ztl holding the fin in position thereon.

The lfrictional ygrip of collar 24 on tube 20l is enhanced `by a fold formation 25 which provides resilience or springiness between two semi-cylindrical portions 24a and Zlib of the collar. The fold formation 25 extends generally diametrically outwardly Ifrom the collar, preferably along the major axis of the rectangular iin. The collar is formed with a dimension measured in a direction at right angles to fold. 25, `slightly less than the linal diameter of the tube 20. As iin 22 is slipped on the tube, collar portions 24a and 24h are spread against the spring action of fold 25' insuring a tight fit of the n on the tube.

Fold 25 is made up of two portions 26 and 27. The surfaces of lirst fold portion 26 are preferably formed tightly against each other for maximum spring effect at crease 28. In general, the portion 25 of the fold extends beyond the `outer edge 24C of the collar. The surfaces of fold portion 27, between portion 26 and the body of lin ZZ are spaced apart, as indicated in the drawings. The space between the surfaces of second fold portion 27 is preferably such that it will receive the rst fold portion 26 of an adjacent fin with the folds arranged in a nested formation. This keys the ns together for alignment and adds strength to the entire assembly. The interengagement of the fold surfaces of adjacent fins also aids in proper spacing between the fins.

With cer-tain alloys of light gauge aluminum, the tins have a tendency to slide toward each other, the portion 27 of the fold 25 of one lin forcing the fold of the next lin apart, loosening the grip of the collar 24 of the next fin. In some cases, all the fins may slide to one end of the tube. FIGURE 5 illustrates a modification in which each of the iins 22 is provided with an extension portion 29 projecting from iboth vertical edges of the iin toward the next adjacent tin and having an inturned flange 29a which bears against the adjacent iin, maintaining the desired separation between fins and preventing fold Z5 from aoaaoie 3 penetrating the fold of the next iin so far that the fold is opened.

In some cases it may be desirable to utilize the fold structure of FIGURES l-4 to position fins 22 on tube `Zt during manufacture and to secure `the fins to the tube as by spot welding or lbrazing in the manner indicated at 3i?, FIGURE 4.

The tins 22 are preferably manufactured in a two-step die-cutting and forming operation, as from a continuous strip of material, for example aluminum. The tirst step, a die-cutting operation, accomplishes several things. First, the proper size of the fin is trimmed or cut from a strip of stock material. Second, and as best seen in FIGURE 6, a channel or rib 3l generally semicircular in section is stamped in the blanks, from which the fold 25 is later formed. A die cuts the opening 32 which will receive tube Ztl and at the same time makes an initial draw of the iin material producing a generally conical surface 32a from which collar 24 is formed. The undersurface of the iin blank adjacent opening 32 is not supported during the cutting and drawing .in what may be described as a freedraw operation. This results in improved physical characteristics of the collar 32a, With less likelihood of stresses or rupturing of the material during subsequent iformings, than if the draw were made against a solid support.

In the second step of the manufacture of the ns, the walls of channel i are forced together, as by a stamping operation, providing the fold configuration of FIGURE 3. A blade inserted into the fold during stamping determines the spacing between the surfaces of the second fold portion Z7. A pilot rod having a slightly smaller diameter than the finished diameter of tube Ztl is positioned inside collar surface 32a during the stamping operation.

The heating unit itself is assembled by positioning the element 21 inside tube Ztl and filling the tube with the granular insulating material, as magnesium oxide. The tube ends are sealed and the tube swaged or rolled, reducing the tube diameter and compacting the insulating material. The fins, either singly or several at a time, are slipped over the end of the tubes, forcing opposed portions Zdrz and 2d!) of collar 24 apart against the spring action of fold 25 so that the collar tightly grips the outer surface of the tube. The tins may be slipped along the surface of the tube to a desired position.

Preferably, the material from which the fins are formed is initially without substantial resilience, and might be classed as dead soft. However, the operations of forming the fold work the material providing the necessary resilience to effect the desired springiness of the fold.

As a specific example, a tube initially 5/8" in diameter might be swaged to a diameter of from 0.490 to 0.495 inch. For this tube, the pilot rod used in forming the collar would have a diameter of the order of 0.487", slightly less than the final diameter of the tube.

FGURES 9 and i() illustrate an improved end member for an electrical tube heater. In the past, end members for the tubes have had a tendency to pop-out during the swaging operation because of the internal pressures set up in the tube. The end member 35 is cup-shaped in configuration having a generally cylindrical wall portion 36 and a closed end portion 37 Formed in the center of end portion 37 is a dimple or depression 38. End member 35 is mounted in the end of tube Ztl and opens outwardly therefrom the dimple or depression 38 extending toward the open tube end, as illust-rated in the drawings. Cylindrical portion 36 of the end member is secured to the wall of tube 2t? as by welding. With this construction of the end member, the dimple 38 deepens during the swaging operation to accommodate the pressures set up in the iiller material, FIGURE 9.

FIGURES 11 and 12 illustrate a modification of the invention in which a n ttl is mounted on a tubular heating unit 4l. The fin has a collar portion 42 defining tubereceiving opening 43. The `tins are slipped over tube 41 and staked in place, las by a stamping operation which l forms yspaced flat surfaces in both the collar 42 and tub( 4I, as indicated at 43. A fold 44 is provided in the fin, extending diametrically outwardly from the collar 4Z adding .strength to the fin body.

While I have shown .and described certain embodiments of my invention, yit is to be understood that it is capable of many modifications. Changes therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

I claim:

1. A heating unit comprising, a tubular heating element having a plurality `of tins thereon each comprising -a plate of heat conductive material with a tube receiving opening therein surrounded by a `collar portion which frictionally engages the surface of the tube, and a fold formed in each plate extending outwardly from said collar, said fold having a first portion with closely spaced surfaces adjacent the crease of the fold and a second portion comprising spaced apart surfaces between 'the first portion and the plate, the first portion of the fold of one iin nesting in the second portion of the fold of the adjacent iin, keying the fins together and aligning them on the tubular element.

2. An end member for a tubular heating unit comprising la cup-shaped element with a bottom pontion and rim, said bottom portion having a generally semi-toroidal edge portion substantially tangential to and extending inwardly from said rim and substantially tangential to a dimple generally centrally disposed in the bottom portion and extending therefrom in the same direction as the rim.

3. A heating unit comprising: a tube; ian electrical heating element lin said tube and surrounded by compacted insulating material; and a cup-shaped end member for said tube having a bottom portion and a rim portion extending from said bottom portion toward the open end of said tube, and a dimple in the bottom portion, said dimple extending toward the open end of said tube.

4. A heating unit comprising, a tubular heating element having a plurality of fins thereon each comprising `a plate of heat conductive material with a tube receiving opening therein surrounded by a collar portion which frictionally engages the 4surface of the tube, said fins having key portions dened by folds in said lins extending `outwardly a substantial distance from said tube :and keyed to an adjacent iin for maintaining alignment of said tins.

5. A heating unit comprising, 4a tubular heating element having a plurality of fins thereon each comprising a plate `of heat conductive material with a tube receiving opening therein surrounded by a collar pont-ion which fniotionally engages the surface of the tube, said fins having key portions detined by a portion of leach iin folded upon itself, said key portions extending outwardly la substantial distance from said tube and keyed to an adjacent iin for maintaining alignment 'of said fins.

6. A heating unit comprising, a tubular heating element having a plurality of fins thereon each comprising a plate of heat conductive material with a tube receiving opening therein surrounded by a collar portion which friotionally engages the surface of the tube, said fins having key portions deiined by a portion of each iin folded upon itself to define a slot, said key portions extending outwardly a substantial distance from said tube and said tins being keyed together for maintenance of alignment of said fins by the reception in said slots of a similar folded portion of an adjacent tin.

7. A heating unit comprising, a tubular heating element having a plurality of fins thereon each comprising a plate of heat conductive material with a tube receiving opening therein surrounded by a collar pontion which frictionally engages the surface of the tube, said tins having key portions defined by means including a resilient portion `of the respective fin folded upon itself to urge said collar into tight engagement with said tube, said key portions extending outwardly a substantial distanceV from said 5 tube and keyed to an adjacent n for maintaining aignnient of said ns.

8. The heating unit of claim 7 in which said key portions are folded to define na slot receiving .a similar folded portion `of `an adjacent `iin thereby keying `said ns to each other.

References Cited in the file of this patent UNITED STATES PATENTS 982,735 McElroy Jian. 24, 1911 1,052,998 Besley Feb. 11, 1913 1,320,430 Wheeler Nov. 4, 1919 1,673,370 Murray June 12, 1928 1,710,579 Henshall Apr. 23, 1929 1,720,334 Langensiepen July 9, 1929 1,791,517 Trane Feb. 10, 1931 1,902,350 Whitaker Mar. 21, 1933 1,997,844 Wiegand Apr. 16, 1935 6 Abbott Dec. 31, 1935 Young et al. Aug. 25, 1936 Cole et al. Aug. 3, 1937 Cobb Aug. 10, 1937 Wiegand Aug. 22, 1939 Wiegand Aug. 22, 1939 `Brede-son Jan. 5, 1943 Shannon Nov. 2, 1948 Powell etal f June 19, 1951 `LacyJHulbert et al. Apr. 11, 1952 Plumeri Oct. 27, 1953 Gex-mon Aug. 20, 1957 Dicome Oct. 22, 1957 Ayling July 28, 1959 Dubin etal Aug. 11, 1959 Sawyer Nov. 21, 1961 FOREIGN PATENTS France Sept. 20, 1905 

4. A HEATING UNIT COMPRISING, A TUBULAR HEATING ELEMENT HAVING A PLURALITY OF FINS THEREON ECH COMPRISING A PLATE OF HEAT CONDUCTIVE MATERIAL WITH A TUBE RECEIVING OPENING THEREIN SURROUNDED BY A COLLAR PORTION WHICH FRICTIONALLY ENGAGES THE SURFACE OF THE TUBE, SAID FINS HAVING KEY PORTIONS DEFINED BY FOLDS IN SAID FINS EXTENDING OUTWARDLY A SUBSTANTIAL DISTANCE FROM SAID TUBE AND KEYED TO AN ADJACENT FIN FOR MAINTAINING ALIGNMENT OF SAID FINS. 